The immediate aim of this research is to determine by X-ray crystallographic techniques, utilizing the most recent developments in direct methods of structure determination, the structures of a series of ionophores, ion transport antibiotics and membrane lipids. Because the functional, physical, and chemical properties of a wide spectrum of biological membranes are well defined, there is reason to believe that knowledge of the exact molecular conformation of molecules that act upon and are present in living membranes will provide the key to fully understanding membrane function at a molecular level. The molecular information revealed by studies of ionophore structures and interpreted in the light of spectral data, kinetics studies, and membrane model theory should provide an explanation of ion complexing, transport, and release mechanisms in membranes. This information will be used to test the feasibility of present ion transport and membrane structure models and to suggest modifications in those models. Although initial studies concern antibiotic-induced ion transport, these functions must of necessity be tied to normal membrane transport phenomena. Because membranes through their transport properties can be said to exert some control over almost all cell functions, and because drugs, hormones, and vitamins may have their primary effect upon cell membranes, there is little doubt that a better knowledge of membrane molecular function would contribute substantially to understanding cell function and malfunction, and also normal and cancerous growth.